Several hundred thousand opponents of same-sex marriage have marched in central Paris against a reform the unpopular French government passed last month at the price of deepening political polarisation.

Large park grounds around Les Invalides monument were full of protesters waving pink and blue flags, while far-right activists hung a banner on the ruling Socialist Party headquarters urging President Francois Hollande to quit.

The protests, which began as a grass roots campaign strongly backed by the Roman Catholic Church, have morphed into a wider movement with opposition politicians and far-right militants airing their discontent with Hollande.

Although they have failed to block gay marriage, the protesters hope their renewed show of force will help stop or slow down further laws some Socialists want allowing assisted procreation and surrogate motherhood for gay couples.

Jean-Francois Cope, leader of the opposition UMP party, marched in the demonstration and urged young protesters to join his party to keep up pressure on the left-wing government.

"The next rendez-vous should be at the ballot boxes for the municipal elections," he said, referring to local polls due next year where conservatives hope to profit from the protest movement's unexpectedly strong mobilisation.

While the rally was peaceful throughout much of the day, police said they arrested 96 hardline opponents to the gay marriage law later on for refusing to disperse or occupying private property.

Once the bulk of protesters had gone home, clashes erupted between hardliners wielding sticks and riot police, filling the Invalides Esplanade with tear gas. The violence was less severe than at the end of previous demonstrations, however.

Police said 150,000 marched on Sunday while protest organisers said a million people took part.

WARNINGS OF VIOLENCE IGNORED

Interior Minister Manuel Valls warned protesters not to bring children along because of violence he feared after far-right militants clashed with police at recent rallies. He mobilised 4500 police to secure the event.

Many parents ignored his warnings and some picnicked with children on the lawn at the rally.

"Look, it's perfectly safe here," said Elisabeth Huet from Orleans, who marched along with her adult daughter and three small grandchildren.

A survey published on Sunday showed 53 per cent of those polled support gay marriage and adoption, indicating a slide of about 10 points since the protests began last November. It said 72 per cent thought the protests should stop now.

Plagued by economic recession, unemployment at more than 10 per cent and pressure to reduce the public deficit, Hollande got some respite on Sunday from another poll showing his record low popularity had inched up four points to 29 per cent this month.

While leaders of Hollande's Socialist Party denounced the protest against a law already passed in parliament and validated by the Constitutional Council, the conservative UMP party was split over whether to continue the rallies.